eslint-plugin: refactor to ES2021 and add no-undeclared-imports rule

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/eslint-plugin/lib/getPackages.js

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// @ts-check
+
+/** @type {import('@manypkg/get-packages')} */
+const manypkg = require('@manypkg/get-packages');
+
+/**
+ * @typedef ExtendedPackage
+ * @type {import('@manypkg/get-packages').Package & { packageJson: { exports?: Record<string, string> }}} packageJson
+ */
+
+/**
+ * @typedef PackageMap
+ * @type object
+ *
+ * @property {ExtendedPackage} root
+ * @property {ExtendedPackage[]} list
+ * @property {Map<string, ExtendedPackage>} map
+ */
+
+// Loads all packages in the monorepo once, and caches the result
+module.exports = (function () {
+  let result = undefined;
+  let lastLoadAt = undefined;
+
+  /** @returns {PackageMap | undefined} */
+  return function getPackages(/** @type {string} */ dir) {
+    if (result) {
+      // Only cache for 5 seconds, to avoid the need to reload ESLint servers
+      if (Date.now() - lastLoadAt > 5000) {
+        result = undefined;
+      } else {
+        return result;
+      }
+    }
+    const packages = manypkg.getPackagesSync(dir);
+    if (!packages) {
+      return undefined;
+    }
+    result = {
+      map: new Map(packages.packages.map(pkg => [pkg.packageJson.name, pkg])),
+      list: packages.packages,
+      root: packages.root,
+    };
+    lastLoadAt = Date.now();
+    return result;
+  };
+})();

packages/eslint-plugin/lib/visitImports.js

@@ -0,0 +1,100 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// @ts-check
+
+const getPackages = require('./getPackages');
+
+/**
+ * @typedef LocalImport
+ * @type {object}
+ * @property {'local'} type
+ * @property {string} path
+ */
+
+/**
+ * @typedef InternalImport
+ * @type {object}
+ * @property {'internal'} type
+ * @property {string} path
+ * @property {import('./getPackages').ExtendedPackage} package
+ */
+
+/**
+ * @typedef ExternalImport
+ * @type {object}
+ * @property {'external'} type
+ * @property {string} path
+ * @property {string} packageName
+ */
+
+/**
+ * @callback ImportVisitor
+ * @param {import('eslint').Rule.Node} node
+ * @param {LocalImport | InternalImport | ExternalImport} import
+ */
+
+/**
+ * @param visitor - Visitor callback
+ * @param {import('eslint').Rule.RuleContext} context
+ * @param {ImportVisitor} visitor
+ */
+module.exports = function visitImports(context, visitor) {
+  const packages = getPackages(context.getCwd());
+  if (!packages) {
+    return;
+  }
+
+  function visit(node) {
+    if (!node.source) {
+      return;
+    }
+    const importPath = node.source.value;
+    if (importPath[0] === '.') {
+      return visitor(node, { type: 'local', path: importPath });
+    }
+
+    const pathParts = importPath.split('/');
+
+    // Check for match with plain name, then namespaced name
+    let packageName;
+    let subPath;
+    if (importPath[0] === '@') {
+      packageName = pathParts.slice(0, 2).join('/');
+      subPath = pathParts.slice(2).join('/');
+    } else {
+      packageName = pathParts[0];
+      subPath = pathParts.slice(1).join('/');
+    }
+    const pkg = packages?.map.get(packageName);
+    if (!pkg) {
+      return visitor(node, {
+        type: 'external',
+        path: subPath,
+        packageName: packageName,
+      });
+    }
+
+    return visitor(node, { type: 'internal', path: subPath, package: pkg });
+  }
+
+  return {
+    ImportDeclaration: visit,
+    ExportAllDeclaration: visit,
+    ExportNamedDeclaration: visit,
+    ImportExpression: visit,
+  };
+};